1. Field of the Invention
This invention relates to blowout preventors for oil and gas wells and more particularly, to a rotating blowout preventor mounted on the well head or on one of the primary blowout preventors bolted to the well head, to pressure seal the interior of the well casing and permit forced circulation of drilling fluid through the well during the drilling operation. The rotating blowout preventor of this invention includes an outer housing attached to the well head or to one of the primary blowout preventors and an inner housing which is journalled for rotation in the outer housing and encloses a stripper rubber. The stripper rubber is designed to seal against a drill pipe in the drilling string by means of well bore pressure and hydraulic pressure maintained on the upper and middle portions of the stripper rubber by means of a hydraulic pump. In a preferred embodiment the hydraulic pressure applied to the stripper rubber is maintained above, and most preferably, about ten percent above the well bore pressure at all times and the well bore pressure is manually or automatically monitored to insure an excess of external hydraulic pressure appllied to the upper portion of the stripper rubber. In a preferred embodiment a J-tool device is attached to the stripper rubber for receiving a pipe clamp attached to a drill pipe in the drilling string and lifting the stripper rubber from the inner housing when it is desired to remove the stripper rubber from the rotating blowout preventor. Release of a bayonet coupling in the J-tool and stripper rubber top retaining plate facilitates removal and repair or replacement of the stripper rubber without the necessity of removing the inner housing of the rotating blowout preventor from the outer housing or the rotating blowout preventor from the well.
Oil, gas, and other wells are typically drilled with the drill bit connected to a hollow drilling string which is inserted into a well casing cemented in the well bore. A drilling head is attached to the well casing, well head or associated blowout preventor equipment for the purpose of sealing the interior of the well casing from the surface and facilitating forced circulation of drilling fluid through the well while drilling in the well. In the more commonly used forward circulation drilling technique, drilling fluid is pumped downwardly through the bore of the hollow drill string, out of the bottom of the bore and then upwardly through the annulus defined by the drill string and the interior of the well casing and subsequently from the well string side outlet at the housing. In reverse circulation, the drilling fluid is pumped directly through the side outlet or mud return and the annulus between the drill string and the well casing and subsequently upwardly through the drill string bore from the well.
Prior art drilling heads typically include a stationary body which carries a rotatable spindle operated by a kelly apparatus. One or more seals or packing elements, sometimes referred to as stripper packers or stripper rubbers, is carried by the spindle to seal the periphery of the kelly or the drive tube or sections of the drill pipe, whichever may be passing through the spindle, and thus confine the fluid pressure in the well casing to prevent the drilling fluid from escaping between the rotating spindle and the drilling string. As modern wells are drilled to ever deeper depths, greater temperatures and pressures are encountered, thus sometimes causing steam or hot water vapor at the drilling head. These rigorous drilling conditions pose increased risks to rig personnel from accidental scalding, burns or contamination by steam, hot water and hot caustic well fluids.
2. Description of the Prior Art
Among the patents which relate to rotating blowout preventors are the following: U.S. Pat. No. 3,128,614, dated Apr. 14, 1964 to Auer; U.S. Pat. No. 3,868,832, dated Mar. 4, 1975, to Biffle; U.S. Pat. No. 3,965,987, dated Jun. 29, 1976, to Biffle; U.S. Pat. No. 4,157,186, dated Jun. 5, 1979 to Murray, et al; U.S. Pat. No. 4,304,310, dated Dec. 8, 1981 to Garrett; U.S. Pat. No. 4,312,404, dated Jan. 26, 1982 to Morrow; U.S. Pat. No. 4,363,357, dated Dec. 14, 1982, to Hunter; U.S. Pat. No. 4,383,577, dated May 17, 1983, to Pruitt; U.S. Pat. No. 4,398,599, dated Aug. 16, 1983, to Murray; U.S. Pat. No. 4,406,333, dated Sep. 27, 1983, to Adams; U.S. Pat. No. 4,416,340, dated Nov. 22, 1983 to Bailey; U.S. Pat. No. 4,423,776, dated Jan. 3, 1984, to Wagoner et al; U.S. Pat. No. 4,783,084, dated Nov. 8, 1988 to Biffle; U.S. Pat. No. 4,448,255, dated May 15, 1984, to Shaffer et al; U.S. Pat. No. 4,531,580, dated Jul. 30, 1985 to Jones; U.S. Pat. No. 4,531,591, dated Jul. 30, 1985 to Johnston; U.S. Pat. No. 4,745,970, dated May 24, 1988 to Bearden et al; U.S. Pat. No. 5,022,472, dated Jun. 11, 1991 to Bailey, et al; and U.S. Pat. No. 5,279,365, dated Jan. 18, 1994 to Yenulis et al.
It is an object of this invention to provide a rotating blowout preventor which is characterized by a blowout preventor outer housing, an inner housing journalled for rotation inside the outer housing, a stripper rubber removably seated in the inner housing for rotating with the inner housing and the drilling string in the well, and a hydraulic pressurizing system communicating with the inner housing and stripper rubber for maintaining a selected level of hydraulic pressure on the stripper rubber and causing the stripper rubber to tightly seat against a drill pipe in the drilling string.
Another object of this invention is to provide a new and improved rotating blowout preventor for mounting on the well head or on one or more primary blowout preventors mounted on the well head, which rotating blowout preventor is characterized by a stripper rubber removably contained inside a rotating inner housing designed to rotate with respect to an outer housing; a brake for arresting rotation of the inner housing and stripper rubber; and a stripper rubber-removing tool attached to the top of the stripper rubber by means of a bayonet coupling and fitted with a J-slot for receiving a drill pipe clamp attached to the drill string and removing the stripper rubber from the inner housing at selected maintenance or replacement intervals.
A still further object of this invention is to provide a new and improved rotating blowout preventor for oil and gas wells, which device is characterized by an outer housing adapted for bolting to the well head or to one of a pair of primary blowout preventors mounted on the well head, an inner housing journalled for rotation in the outer housing and a reinforced stripper rubber removably attached to the inner housing, along with a hydraulic brake for arresting rotation of the inner housing and stripper rubber and a pump and sensing system for sensing the well bore pressure applied to the lower portion of the stripper rubber when the rotating blowout preventor is deployed in the well and pumping hydraulic fluid through the outer housing and inner housing against the middle and upper portions of the stripper rubber to maintain hydraulic pressure on these areas of the stripper rubber in excess of the well bore pressure applied to the lower portion of the stripper rubber.
Yet another object of this invention is to provide a technique for maintaining the stripper rubber of a rotating blowout preventor tightly in contact with the rotating drilling string and minimize rotation of the drilling string with respect to the stripper rubber, which technique includes the steps of removably mounting a pleated reinforced stripper rubber inside a rotating inner housing encircling a drill pipe, wherein the inner housing is journalled for rotation inside an outer housing; providing a brake for selectively arresting rotation of the inner housing and stripper rubber; providing a hydraulic pressurizing system communicating with the middle and upper portion of the stripper rubber for pressurizing the upper and middle portion of the stripper rubber and maintaining the stripper rubber tightly in contact with the drill pipe at a pressure above the well bore pressure operating on the bottom segment of the stripper rubber; and providing a lifting tool attached to the stripper rubber and a clamp for attachment to the drill pipe and lifting tool for selectively removing the stripper rubber from the inner housing by lifting the drilling string.